1. Field of the Invention
The invention relates generally to a tapered roller bearing, and more specifically to a tapered roller bearing incorporated in, for example, a final reduction gear unit of an automobile and lubricated with oil stored in the final reduction gear unit.
2. Description of the Related Art
FIG. 11 illustrates a conventional tapered roller bearing. The tapered roller bearing includes an outer ring 72, an inner ring 82, a plurality of tapered rollers 74, and a cage 87. The outer ring 72 has an outer raceway surface 71 formed on its inner peripheral face. The inner ring 82 has an inner raceway surface 81 formed on its outer peripheral face. The tapered rollers 74 are rollably disposed between the outer raceway surface 71 and the inner raceway surface 81. The cage 87 holds the tapered rollers 74 at equal intervals in the circumferential direction of the tapered roller bearing.
Tapered roller bearings are widely used because they are compact, able to bear large radial loads and large axial loads, and usable under high-speed rotation. However, toque loss of the tapered roller bearings is larger than that of ball bearings. Therefore, reduction of toque is a matter to be addressed from the viewpoint of energy saving.
The tapered roller bearing is configured such that, under the pumping action resulting from the rotation of the tapered roller bearing, the oil introduced into the tapered roller bearing through a clearance between a small-diameter-side end portion 88 of the cage 87 and an inner ring outer periphery 85 and a clearance between the small-diameter-side end portion 88 of the cage 87 and an outer ring inner periphery 75 flows through the tapered roller bearing. The stirring resistance of the oil largely contributes to an increase in the rotary torque of the tapered roller bearing. Japanese Patent Application Publication No. 2005-69421 (JP 2005-69421 A) describes a configuration in which a small-diameter-side portion of the cage 87 is bent radially inward to reduce a clearance between the small-diameter-side portion of the cage 87 and the outer periphery of the inner ring 82 (hereinafter, referred to as “radially-inner clearance”) and to form a labyrinth, in order to appropriately adjust the flow of oil in the tapered roller bearing, thereby reducing the rotary torque. Japanese Patent Application Publication No. 2008-202785 (JP 2008-202785 A) describes a configuration in which means for adjusting a clearance between the small-diameter-side end portion 88 of the cage 87 and the inner periphery of the outer ring 72 (hereinafter, referred to as “radially-outer clearance”) is provided in order to limit the flow of oil through the radially-outer clearance.
In the tapered roller bearing described in JP 2005-69421 A, the inner peripheral face of the small-diameter-side end portion 88 of the cage 87 faces the inner ring outer periphery 85 across a clearance in the radial direction of the tapered roller bearing. A cone front face rib (hereinafter, referred to as “a small rib”) 89 that protrudes outward in the radial direction is formed on the inner ring outer periphery 85. The small-diameter-side end portion 88 of the cage 87 is disposed outward of the small rib 89 in the axial direction of the tapered roller bearing. An axially inner side face of the small-diameter-side end portion 88 faces an axially outer side face of the small rib 89 across a small clearance.
As described above, the labyrinth is formed between the inner peripheral side of the small-diameter-side end portion 88 of the cage 87 and the outer peripheral side of the inner ring 82. The labyrinth makes it possible to reduce the amount of oil flowing into the tapered roller bearing through the clearance located radially inward of the small-diameter-side end portion 88 of the cage 87. By reducing the amount of oil flowing into the tapered roller bearing, that is, into the inside of the tapered roller bearing in which the tapered rollers are disposed, through the radially-inner clearance as described above, it is possible to reduce stirring resistance of the oil, thereby curbing an increase in the rotary torque of the tapered roller bearing.